1. Technical Field
The present invention pertains to improvements in methods and apparatus for producing and collecting surgical sterile slush. In particular, the invention is an improvement of the methods and apparatus disclosed in U.S. Pat. Nos. 4,393,659 (Keyes et al), 4,934,152 (Templeton), 5,163,299 (Faries, Jr. et al), 5,331,820 (Faries, Jr. et al) and the patents cited therein. The disclosures in the aforementioned patents are expressly incorporated by reference herein in their entireties.
2. Discussion of the Prior Art
The above-referenced Keyes et al patent discloses a surgical slush producing system having a cabinet with a heat transfer basin at its top surface. A refrigeration mechanism in the cabinet takes the form of a closed refrigeration loop including an evaporator in heat exchange relation to the outside surface of the heat transfer basin; a compressor; a condenser; and a refrigeration expansion control, all located within the cabinet. A separate product basin is configured to be removably received in the heat transfer basin. Spacers, in the form of short cylindrical stubs or buttons, are arranged in three groups spaced about the heat transfer basin and projecting into the heat transfer basin interior to maintain a prescribed space between the two basins. During use that space contains a thermal transfer liquid, such as alcohol or glycol, serving as a thermal transfer medium between the two basins. A sterile drape, impervious to the thermal transfer medium is disposed between the product basin exterior and the liquid thermal transfer medium to preserve the sterile nature of the product basin. Surgically sterile liquid, such as sodium chloride solution, is placed in the product basin and congeals on the side of that basin when the refrigeration unit is activated. A scraping tool is utilized to remove congealed sterile material from the product basin side to thereby form a slush of desired consistency within the product basin. Some users of the system employ the scraping tool to chip the solid pieces from the basin side.
As noted in the above-referenced Templeton patent, the Keyes et al system has a number of disadvantages. In particular, the separate product basin must be removed and resterilized after each use. Additionally, the glycol or other thermal transfer medium is highly flammable or toxic and, in any event, complicates the procedure. The Templeton patent discloses a solution to these problems by constructing an entirely new apparatus whereby the product basin is eliminated in favor of a sterile drape impervious to the sterile surgical liquid, the drape being made to conform to the basin and directly receive the sterile liquid. Congealed liquid is scraped or chipped from the sides of the conformed drape receptacle to form the desired surgical slush.
The Faries, Jr. et al U.S. Pat. No. (5,163,299) notes that scraping congealed liquid from the drape is undesirable in view of the potential for damage to the drape, resulting in a compromise of sterile conditions. As a solution to the problem, the patent proposes that the drape be lifted or otherwise manipulated by hand to break up the congealed liquid adhering to the drape. Although this hand manipulation is somewhat effective, it is not optimal, and often is inconvenient and constitutes an additional chore for operating room personnel.
The aforesaid Faries, Jr. et al U.S. Pat. No. (5,331,820) addresses the problem of removing the congealed liquid from the sides of the conformed drape receptacle in a surgical slush machine. Specifically, the drape is conformed to a cooled basin to establish a sterile field above the basin. The conformed drape receptacle collects a congealed sterile liquid (e.g., saline) in a sterile slush-like consistency. The congealed liquid tends to attach to sides of the drape receptacle in large clumps or pieces rather than automatically collecting within the drape receptacle interior. The Faries. Jr. et al U.S. Pat. No. (5,331,820) discloses a technique for automatically manipulating the drape relative to the basin wall to thereby cause the congealed liquid to detach from the drape receptacle sides and collect interiorly as desired slush. Briefly, the technique includes reciprocating the bottom of the conformed drape receptacle up and down to thereby loosen attached pieces of frozen saline from the sides of the drape receptacle.
The present invention is an improvement in the drape for use in conjunction with the aforementioned technique of reciprocating the bottom of the drape receptacle up and down to loosen pieces of frozen saline from the sides of the drape receptacle. It has been discovered that drapes having either a preformed container portion, made of other drape materials or formulations of the drape material currently being used (described below), or made of the conventional drape material and having a coefficient of friction less than approximately 0.4 when measured against steel (i.e., the basin) per ASTM 1983, are not effective for having the congealed liquid detached from the sides of the drape receptacle by reciprocating the bottom of the drape receptacle. Typically, the reciprocating motion is accomplished by a substantially circular plate or disc disposed at the bottom of the basin beneath the drape. The plate is reciprocally driven up and down to manipulate the drape receptacle relative to the basin to dislodge the congealed liquid from the sides of the drape receptacle. However, if the drape has a preformed container portion, the container portion becomes contoured to the basin and does not permit air to flow beneath the drape. The reciprocating motion of the plate creates a suction and draws the air between the drape and the plate, and the drape itself, beneath the plate. Similarly, if the drape is constructed of other drape materials or formulations of the conventional drape material, or the conventional drape material having a coefficient of friction less than approximately 0.4 as measured against steel per ASTM 1983, the resultant drape is slippery and becomes substantially contoured the basin to inhibit air from flowing beneath the drape. The suction created during the plate's reciprocating motion tends to draw the drape beneath the plate as described above. When the drape is positioned beneath the plate, the plate only manipulates that portion of the drape receptacle in contact with the plate, thereby leaving substantial parts of the drape receptacle unmanipulated with the congealed liquid attached.